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Old 09-05-2019, 07:11 PM   #1
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Converter output amps lower than specs

I noticed on my Victron BMV712 battery monitor that I am getting about 15 A when charging batteries when plugged in . I would’ve expected higher amps since the converter is rated for 55 amp output. It is the stock airstream WFCO WF-89xx series converter.

What am I missing? Here’s a screenshot of the battery monitor readings at rest (not charging).
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Old 09-05-2019, 07:22 PM   #2
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The amount of amps is dependent on the existing state of charge in your batteries. If the batteries are low, say 50% charge, then your converter will put out more amps than when your batteries are already at a 90% charge.
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Old 09-05-2019, 07:53 PM   #3
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Thanks. I guess I expected that at 64% soc more amps would be delivered to speed up the charging process.
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Old 09-05-2019, 08:35 PM   #4
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Hi

Without a snapshot of the 712 while charging it's a bit tough to guess what's going on.

The typical converter charger does indeed "taper" the current it puts out as the voltage goes up. If the battery is down around 9 or 10V it should try to put the full rated current into the battery. As it goes above that ( = zero charge) point, the current seems to cut back.

There are indeed converters out there that are much more aggressive. They also are much more expensive and weigh a lot more ..... wonder what that means ....

Bob
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Old 09-06-2019, 06:00 PM   #5
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It is my observation that the stock charger doesn't do a good job charging the batteries. My solar puts 30A on a sunny day.

My thinking is that there should be 2 modes for charging the batteries: 1) when it is plugged in to the power all the time. It needs a slow almost a trickle charge. 2) when I dry camp and run the generator. I want a very fast high amp charge, but for a short time. I wonder if there is a single charger that can handle both situations.
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Old 09-06-2019, 06:38 PM   #6
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My unit is older, but some charging principles apply, regardless.....
Predominantly, a slow charge is ALWAYS preferable to a fast charge, as it relates to the duration of the charge and the stress on the batteries.....for this reason, most converters are going to charge slowly, unless it thinks there is an urgent situation at hand, and since it is an electronic device, its thinking is limited !
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Old 09-06-2019, 06:39 PM   #7
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Originally Posted by chugchug View Post
It is my observation that the stock charger doesn't do a good job charging the batteries. My solar puts 30A on a sunny day.

My thinking is that there should be 2 modes for charging the batteries: 1) when it is plugged in to the power all the time. It needs a slow almost a trickle charge. 2) when I dry camp and run the generator. I want a very fast high amp charge, but for a short time. I wonder if there is a single charger that can handle both situations.
Hi

If your stock solar setup charges at a 30A rate, you have the world champion of stock solar setups. If it puts in 30AH per day .... maybe not so much. ( A = amps = amount of current going in at one time, AH = amp hours = amps X hours of charge)

=====

If you have a lead acid battery, there is only so much the charger can do. If it keeps up a high charge rate past a certain point it pretty much destroys the battery. Yes, you will charge it faster, no it will not last very long if you do ....

Bob
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Old 09-06-2019, 06:42 PM   #8
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Here are my readings from the battery monitor. First with no generator, then immediately after starting the Gen, and finally after an hour of running.

I was so pleased with the near 30 amps when starting but it quickly dropped.
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Old 09-06-2019, 07:00 PM   #9
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Originally Posted by uncle_bob View Post
Hi

If your stock solar setup charges at a 30A rate, you have the world champion of stock solar setups. If it puts in 30AH per day .... maybe not so much. ( A = amps = amount of current going in at one time, AH = amp hours = amps X hours of charge)

=====

If you have a lead acid battery, there is only so much the charger can do. If it keeps up a high charge rate past a certain point it pretty much destroys the battery. Yes, you will charge it faster, no it will not last very long if you do ....

Bob
To be clear - the solar is aftermarket 4 stage charger and it is A not AH.

I agree that it is better to charge slowly, but if the charge goes to zero before the night is out, then it was too slow. I hate getting up at the middle of the night to fire up the generator.
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Old 09-06-2019, 07:12 PM   #10
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Originally Posted by Omnial View Post
Here are my readings from the battery monitor. First with no generator, then immediately after starting the Gen, and finally after an hour of running.

I was so pleased with the near 30 amps when starting but it quickly dropped.
You notice that the charge current quickly drops as the battery voltage rises above 13v. My stock converter does the same.

I searched the internet and it seems a 4 stage charger in the initial stage Boost (or Bulk) should keep the current constant and let the voltage rise to about 14.4-14.6v and only then switch to Absorption stage where the voltage stays constant and the current drops. Why the onboard charger no doing that is not clear to me.
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Old 09-07-2019, 09:54 AM   #11
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Originally Posted by Omnial View Post
Here are my readings from the battery monitor. First with no generator, then immediately after starting the Gen, and finally after an hour of running.

I was so pleased with the near 30 amps when starting but it quickly dropped.
Hi

Your battery monitor shows a very typical lead acid charging process. The key thing to look at is the voltage. As the voltage rises, the current drops. That's just how it works.

Bob
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Old 09-07-2019, 09:58 AM   #12
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Originally Posted by chugchug View Post
To be clear - the solar is aftermarket 4 stage charger and it is A not AH.

I agree that it is better to charge slowly, but if the charge goes to zero before the night is out, then it was too slow. I hate getting up at the middle of the night to fire up the generator.
Hi

You keep mentioning "solar" .....

If we are talking about *solar* putting current into a battery, that's not at all the same thing as a converter charger putting in current. A generator runs into a converter / charger to charge the batteries. A solar panel runs into a solar charger to get energy in. Two *very* different things.

To put in 30A of current, you need quite a bit solar setup in terms of number of panels as well as an upgraded charging system. Most of us have gone over to MPPT designs as part of that process.

Bob
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Old 09-07-2019, 01:55 PM   #13
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Originally Posted by Omnial View Post
Here are my readings from the battery monitor. First with no generator, then immediately after starting the Gen, and finally after an hour of running.

I was so pleased with the near 30 amps when starting but it quickly dropped.
What's notable to me on your readings is not so much the current...but the voltage. With my Progressive Dynamics PD4655, if my batteries are at 12.2v (even higher, actually, like 12.5V) when firing up the generator (or plugging in to shore power), the voltage from the charger might start at 13.6, but in short order, figure things out and ramp up to 14.x volts, and stay there for an hour or 4 (depending on beginning SOC), before dropping to 13.6V absorption, and after 24 hours (more or less), down to 13.2v float. I'm not an electrical engineer, but everything I've read states that it takes higher voltage pushing into flooded batteries to get them charged.

That doesn't seem to be the case with yours, which is an anemic 13.02 volts after an hour? Is that the highest it ever gets, or did you note 14.x during that first hour, then it dropped? But even if so, from 14.x to 13.02? That's not even 'float' mode, which should be more like 13.2v. Maybe the new WFCO units have fixed the supposed problem of the old units not dropping to an appropriate 'float' mode and therefore cooking batteries; but they apparently didn't take care of the other end of the spectrum, which is pushing more volts at the batteries in a 'bulk' phase. Or, at least your unit isn't. I'd consider a replacement based on your data. Another nice thing with the PD units is that when recharging out in the field while dry camping, I don't even have to wait for the charger to 'figure out' it needs to increase to 14.4v...you can just press a button and force it in to bulk mode right away, making every minute of generator recharging count.Click image for larger version

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Old 09-07-2019, 03:20 PM   #14
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What's notable to me on your readings is not so much the current...but the voltage. With my Progressive Dynamics PD4655, if my batteries are at 12.2v (even higher, actually, like 12.5V) when firing up the generator (or plugging in to shore power), the voltage from the charger might start at 13.6, but in short order, figure things out and ramp up to 14.x volts, and stay there for an hour or 4 (depending on beginning SOC), before dropping to 13.6V absorption, and after 24 hours (more or less), down to 13.2v float. I'm not an electrical engineer, but everything I've read states that it takes higher voltage pushing into flooded batteries to get them charged.

That doesn't seem to be the case with yours, which is an anemic 13.02 volts after an hour? Is that the highest it ever gets, or did you note 14.x during that first hour, then it dropped? But even if so, from 14.x to 13.02? That's not even 'float' mode, which should be more like 13.2v. Maybe the new WFCO units have fixed the supposed problem of the old units not dropping to an appropriate 'float' mode and therefore cooking batteries; but they apparently didn't take care of the other end of the spectrum, which is pushing more volts at the batteries in a 'bulk' phase. Or, at least your unit isn't. I'd consider a replacement based on your data. Another nice thing with the PD units is that when recharging out in the field while dry camping, I don't even have to wait for the charger to 'figure out' it needs to increase to 14.4v...you can just press a button and force it in to bulk mode right away, making every minute of generator recharging count.Attachment 351566
Hi

If we are talking about the stock converter, it maxes out in the sub 13.6V range. It does not go into a > 14V "equalize" mode.

Bob
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Old 09-07-2019, 03:31 PM   #15
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Hi

If we are talking about the stock converter, it maxes out in the sub 13.6V range. It does not go into a > 14V "equalize" mode.

Bob
The WFCO 8955 that they started using in 2018 claims a bulk charge mode of 14.4, absorption of 13.6, and float of 13.2v. No "desulfation mode" which is what let's PD market theirs as '4 stage'. Either the units don't meet the specs...or the OP has a bum unit, if he's only getting 13.02v after an hour? (Still curious if he got more than that during the first hour.
https://wfcoelectronics.com/product/wf-8955-55-amp/
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Old 09-08-2019, 09:27 AM   #16
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OR the gauge he is pulling his readings from isn't accurate, OR his batteries are damaged and will not accept a full charge. OR something else I haven't thought about yet....
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Old 09-08-2019, 01:16 PM   #17
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Hi

If we are talking about the stock converter, it maxes out in the sub 13.6V range. It does not go into a > 14V "equalize" mode.

Bob
This from the WFCO site:
The WF-8900 Series has revolutionized RV power centers with its lighter weight, decorative doors and superior features. The WF-8955 model provides 55 Amps and a clean, constant 13.6 VDC nominal output, for reliable operation of electronics and appliances. Automatic three-stage charging extends the life of your battery with output voltage modes of 13.2 VDC range “float” mode, 13.6 VDC range “absorption” mode, and a 14.4 VDC range “bulk” charge mode.

That tells me it should be capable of going up to 14.4. However I’ve never seen it go above 13.2 on generator.

I have three lifeline AGM batteries connected in parallel. I also have 360 W of solar on the roof running into the Victron MPPT 100/50 charge controller. I’ve seen voltages in excess of 14 V from that unit.

Here are 3 more screenshots: start of gen charge, 1 hour later still on gen, and shortly after gen turned off.
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Old 09-08-2019, 01:48 PM   #18
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Hi

Again, that all looks pretty typical of what I've seen on the stock converters. Since they are not telling you how and when the gizmo goes into hyperdrive, it may only do it rarely (like after its been on for 48 hours ....). The purpose of boosting above 14V is to equalize the cells. You don't need to / want to do it very often. With AGM's even less so than with flooded cells.

Also keep in mind that when these guys talk about 13.2V, that's at the terminals on the converter / charger. Any wiring drop due to current will decrease what you see at the battery. That said, it's tenth's of volts at normal currents not a volt and a half.

Bob
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